Icarus 221 (2012) 911–924

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Icarus

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Spectral reflectance properties of carbonaceous chondrites: 7. CK chondrites

E.A. Cloutis a,⇑, P. Hudon b,1, T. Hiroi c, M.J. Gaffey d

a Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba, Canada R3B 2E9b Astromaterials Research and Exploration Science Office, NASA Johnson Space Center, Mail Code KR, 2101 NASA Road 1, Houston, TX 77058-3696, USAc Department of Geological Sciences, Brown University, PO Box 1846, Providence, RI 02912-1846, USAd Department of Space Studies, University of North Dakota, PO Box 9008, Grand Forks, ND 58202-9008, USA

a r t i c l e i n f o

Article history:Received 25 June 2012Revised 10 September 2012Accepted 10 September 2012Available online 1 October 2012

Keywords:Asteroids, SurfacesAsteroids, CompositionMeteoritesSpectroscopy

0019-1035/$ - see front matter � 2012 Elsevier Inc. Ahttp://dx.doi.org/10.1016/j.icarus.2012.09.017

⇑ Corresponding author. Fax: +1 204 774 4134.E-mail addresses: e.cloutis@uwinnipeg.ca (E.A. Clo

(P. Hudon), takahiro_hiroi@brown.edu (T. Hiroi), gaffe1 Present address: Department of Mining and M

University, 3610 rue Université, Montreal, QC, Canada

a b s t r a c t

The reflectance spectra of 15 CK chondrites have been measured as part of an ongoing study of carbona-ceous chondrite reflectance spectra. The available sample suite includes multiple grain sizes and sampleswith petrologic grades varying from CK4 to CK6. CK reflectance spectra are all characterized by an olivine-associated absorption band in the 1.05 lm region. Compared to pure olivine, CK spectra are darker, have amore subdued olivine absorption band, and are often more blue-sloped. Reflectance at 0.56 lm variesfrom 9.6% to 22.5%, and olivine band depth varies from 6.7% to 31.0%, for powders that include the finestfraction. With increasing grain size, and exclusion of the finest fraction, CK spectra become darker andmore blue sloped, while the olivine absorption band initially becomes deeper and then shallower. Thepresence of calcium–aluminum inclusions (CAIs), whose abundance varies widely in CKs, does not nor-mally lead to the appearance of a well-defined absorption band in the 2.1 lm region, although the overallblue slope of many CKs is likely attributable to Fe-bearing spinel in CK CAIs. The only consistent spectralfeature that relates to metamorphic grade is that CK6 spectra have uniformly deeper olivine absorptionband than CK4–5.5 spectra. This could be related to various factors such as loss/aggregation of opaquesthat may accompany metamorphism. Comparison of CV and thermally metamorphosed carbonaceouschondrite to CK spectra suggests that metamorphism to between �1000 and 1200 �C is required forCV spectra to match CK spectra; CV spectra are uniformly darker and have shallower olivine absorptionbands than CK spectra.

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1. Introduction

In an ongoing series of papers concerning the spectral reflec-tance properties of carbonaceous chondrites (CCs), this paperfocuses on the CK group. The CK chondrites are interesting froma number of perspectives. In comparison to other CC groups, theCKs have experienced varying degrees of thermal metamorphism,with petrologic grades ranging from �3 to �6 (Kallemeyn et al.,1991; Noguchi, 1993; Geiger and Bischoff, 1995; Brearley andJones, 1998), and evidence of fluid-assisted metamorphism insome cases (Brearley, 2009). Thus they provide insights into hownaturally occurring thermal metamorphism affects CCs, supple-menting the results of laboratory studies and other, generallyungrouped CCs that have also been affected by thermal metamor-phism (e.g., Hiroi et al., 1993, 1996).

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utis), pierre.hudon@mcgill.cay@space.edu (M.J. Gaffey).aterials Engineering, McGillH3A O5C.

CK chondrites are highly oxidized and generally range betweenpetrologic grades 3 and 6, with high modal abundances of magne-tite – the most common opaque phase – (1.2–8.1 vol.%) comparedto CO, CM, and CV chondrites and high olivine Fa contents (Fa28–33)(Noguchi, 1993; Geiger and Bischoff, 1995; Huber et al., 2006).Metamorphism under oxidizing conditions is also suggested bythe possible presence of Fe3+ in low-calcium pyroxenes and spinels,and abundant Ni in olivines (Noguchi, 1993). Metamorphism alsoleads to Fe enrichment in CAIs (Chaumard et al., 2009).

The CKs have been linked to CVs, and possibly COs, on the basisof a number of criteria. These include compositional, textural, andoxygen isotope similarities to CVs and COs (Kallemeyn et al., 1991).Compositional similarities include elemental abundance patterns,refractory lithophile and siderophile abundances similar to COsand CVs (Kallemeyn et al., 1991). Differences between CK versusCV3OxA groups include lower chondrule/matrix ratios, lower C con-tent, and lower CAI abundances (<3 vol.%) in CKs (Greenwood et al.,2003).

The effects of thermal metamorphism include CK volatile pat-terns that are similar to, but lower than CV patterns (Kallemeynet al., 1991), and reverse zoning in plagioclase (Noguchi, 1993).Mineralogic and petrologic differences, as well as similarities in

Table 1Petrographic characteristics of C-chondrite groups. Source: Brearley and Jones (1998),Neff and Righter (2006), and Rubin (2010).

Group Chondruleabundance(vol.%)

Matrixabundance(vol.%)

Refractoryinclusionabundance(vol.%)

Metalabundance(vol.%)

Chondrulemeandiameter(mm)

CI �1 >99 �1 0 –CM 20 70 5 0.1 0.3CR 50–60 30–50 0.5 5–8 0.7CO 48 34 13 1–5 0.15CV 45 40 10 0–5 1.0CK 15 50–79 4 <0.01 0.7CH �70 5 0.1 20 0.02

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other properties as described above, have led a number of investi-gators to suggest that CKs may be metamorphosed CVs (e.g.,Greenwood et al., 2003, 2004, 2010; Devouard et al., 2006;Isa et al., 2011). Other data, such as induced thermoluminescencesuggest a lack of genetic links between CVs and CKs (Guimonet al., 1995). CKs have also been tentatively linked to Eagle Stationpallasites (Humayun and Weiss, 2011).

Spectral reflectance data for CKs have been limited. Salisburyand Hunt (1974) found that the <74 lm spectrum of Karoondahas among the shallowest 3 lm absorption band and flattest0.5–0.6 lm interval. A <74 lm spectrum of Karoonda (Salisburyet al., 1975) was found to have 13% reflectance at 0.6 lm, a nearlyflat 0.5–0.6 lm interval, and a very weak 1 lm region olivineabsorption band. Hiroi et al. (1993) presented reflectance spectrafor <125 lm powders of ALH 85002 (CK4) and Y-693 (CK4). Bothshowed blue-sloped spectra over the 0.5–2.5 lm interval and anolivine-like absorption band near 1.05 lm. Hiroi et al. (1996) pre-sented an extended reflectance spectrum of Y-693 (0.3–3.6 lm)which also displayed an olivine-like absorption feature centerednear 1.05 lm and a subdued 3 lm water-associated absorptionband. Its 0.7 and 3 lm band strengths were similar to a sampleof the Murchison CM2 chondrite heated to 500 �C. Mothé-Dinizet al. (2008) conducted a comparison of Eos asteroid family mem-bers to a number of CCs. They found that a number of Eos familymembers were well matched by CK4 and CK5 chondrites in thenear infrared region, but differed in the visible region.

Given the general lack of published CK spectra, relationshipsbetween CK spectra and petrography, and the need to improvepossible CK parent body identifications, we undertook this com-prehensive study of CK reflectance spectra. The next section de-scribes the mineralogy/petrology of CKs (in order to establish abasis for interpreting CK spectra), followed by a description ofthe samples used in this study and our experimental procedure,and a description and discussion of CK reflectance spectra.

2. Mineralogy/petrology of CK chondrites

2.1. Overview

Some of the major characteristics of CK chondrites relative toother CC groups are presented in Table 1. Selected CK modal abun-dances are presented in Table 2. CK meteorites are highly oxidizedwith high modal abundances of magnetite, trace amounts of Fe–Nimetal, and high olivine Fa content (Fa28–33) (Geiger and Bischoff,1995; Huber et al., 2006). They contain 10–15 vol.% chondrules(Kallemeyn et al., 1991). Most of the Fe in CKs occurs in magnetiteand in FeO-rich mafic silicates, primarily olivine (Kallemeyn et al.,1991; Huber et al., 2006).

2.2. Matrix

CK matrices are dominated by equilibrated olivine (Fa�29–33),plagioclase, low-Ca pyroxene (Fs23–29), and minor magnetite(mainly fine-grained (<few microns)) and rare sulfides (Kallemeynet al., 1991; Noguchi, 1993). CK matrix is compositionally similarto CVs and COs, but generally more highly metamorphosed. Thematrix consists of two types of materials: (1) 90 vol.% is composedof olivine, plagioclase, magnetite and sulfides; (2) 10 vol.% is com-posed of augite, low-Ca pyroxene, anhedral olivine (�Fa29) andmagnetite (Buseck and Hua, 1993).

2.3. Opaque phases

The major opaque phases are magnetite and pentlandite, andmany magnetite grains contain exsolution lamellae of ilmenite

(Noguchi, 1993; Huber et al., 2006). Magnetite, with exsolvedilmenite and spinel, is the most abundant opaque mineral in CKs,comprising 1.2–8.1 vol.% (Geiger and Bischoff, 1995). It occurs lar-gely as micron-sized grains dispersed throughout the meteoriteand as rounded larger aggregates (Geiger and Bischoff, 1995).Sulfides are present as small grains (mostly 10–30 lm in size)homogeneously distributed throughout these meteorites (Geigerand Bischoff, 1995). Compared to CO, CM, and CV chondrites, CKshave a higher magnetite abundance (Noguchi, 1993; Geiger andBischoff, 1995; Huber et al., 2006).

2.4. CAIs

CAI abundances vary widely in CKs (Kallemeyn et al., 1991;Noguchi, 1993; Neff and Righter, 2006; Hezel et al., 2008), withsome CKs having CAI abundances as high as Allende (Hezel et al.,2008), and ranging up to 13 area% (Keller, 1992; Neff and Righter,2006; Chaumard et al., 2011). Major CAI minerals include plagio-clase and clinopyroxene/fassaite (dominant), and spinel and mag-netite (Brearley and Jones, 1998; Chaumard et al., 2009, 2011).Spinels are invariably Fe-bearing (Brearley and Jones, 1998). Com-positionally, increasing metamorphism leads to Fe enrichment inCAIs (Chaumard et al., 2009, 2011). Keller (1992) and Keller et al.(1992) found numerous melilite-free, Fe-spinel-bearing CAIs inthe Maralinga CK4 chondrite; abundance is on the order of 1.5%,but the CAIs are not homogeneously distributed in the meteorite.

2.5. Mafic silicates

Olivine Fa contents are �29–33, and low-Ca pyroxene is gener-ally Fs23–29 (Kallemeyn et al., 1991; Noguchi, 1993; Brearley andJones, 1998). The groundmass and chondrules are dominated byolivine (Kallemeyn et al., 1991). Pyroxenes occur as minor to acces-sory phases (Brearley and Jones, 1998). Both low and high-Ca con-tent pyroxenes are present. Low-Ca pyroxene compositionsaverage Fs17–27 Wo1–2; high-Ca pyroxenes average Fs11 Wo44–47

(Brearley and Jones, 1998). The inferred presence of Fe3+ in low-Ca pyroxenes contained in matrix plagioclases is consistent withmetamorphism under high oxygen fugacities (Noguchi, 1993).

2.6. Thermal metamorphism

The effects of increasing thermal metamorphism include an in-crease in olivine and pyroxene compositional homogeneity, loss ofglass, increase in plagioclase grain size, blurring of chondrule bor-ders, and coarsening of interchondrule matrix (Kallemeyn et al.,1991; Noguchi, 1993; Huss et al., 2006).

2.7. Darkening – shock

CK chondrites are unexpectedly dark (Salisbury et al., 1975).Brearley and Jones (1998) noted that all CK chondrites contain

Table 2Compositional data for CKs included in this study. Source: Geiger and Bischoff (1995) and Neff and Righter (2006).

Meteorite Type Chondrules (vol.%) Opaques (vol.%) CAIs Matrix (vol.%) Magnetite (vol.%) Sulfides H2O Olivine Fa Pyroxene Fs

A-881551 CK6 11 5.3 wt.% 2.0 wt.% 33A-882113 CK4 4.7 wt.% 3.1 wt.% 21.4 22.6ALH 85002 CK4 3.7 0.6 vol.% 29 26DAV 92300 CK4 26 26EET 83311 CK5 6.6 0.5 vol.% 31EET 87526 CK5 29 24EET 87507 CK5 0.2 areal% 3.1 <0.1 vol.% 32 28EET 87860 CK5/6 6.9 11.8 10.7 vol.% 70.7 3.9 0.6 vol.% 28 28EET 92002 CK4 32Karoonda CK4 15 6.8 1.3 vol.% 33 8–28LEW 87009 CK6 0 4.0 n.d. 79.0 4.6 0.7 vol.% 31PCA 91470 CK4 33Y-693 CK4/5 11 22.9 n.d. n.d. 5.7 0.8 vol.% 0.18 wt.% 29 26Y-82102 CK5 29.5 23Y-82103 CK5 29.8 25.1

Meteorite C content (wt.%) S content (wt.%)

ALH 85002 0.006 1.86EET 83311 0.04 1.98EET 87526 0.007 1.9EET 87860 0.03EET 92002 0Karoonda 0.07 1.4LEW 87009 0.04Y-693 0.06 1.6

n.d.: not determined.

Table 3CK reflectance spectra from RELAB and previous studies.

Meteorite andpetrologic grade

Grain size (lm) Source

A-881551 (CK6) <125a This studyA-882113 (CK4) <125a This studyALH 85002 (CK4) Unknown, <25, 25–45, 45–75,

75–125, <75, <125, <180This study and Hiroiet al. (1993)

DAV 92300 (CK4) <75 This studyEET 83311 (CK5) <75 This studyEET 87526 (CK5) Unknown, <63 This studyEET 87507 (CK5) <125 Hiroi et al. (1996)EET 87860 (CK5/6) Unknown, <63 This studyEET 92002 (CK4) <500 This studyKaroonda (CK4) <74 Salisbury et al.

(1975)<150 Gaffey (1974) – 2

spectraLEW 87009 (CK6) Unknown, <63, <125 This study, Hiroi

et al. (1996)PCA 91470 (CK4) <75 This studyY-693 (CK4/5) <125 Hiroi et al. (1993)Y-82102 (CK5) <125a This studyY-82103 (CK5) <125a This study

a Spectrum only available from 0.3 to 0.88 lm.

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regions of shock-induced, darkened silicates, containing tiny grainsof magnetite and pentlandite. Hashiguchi et al. (2008) suggestedthat this darkening is due to shock-darkening, specifically the for-mation of vesicles and complex networks of veinlets. The vesicularolivine contains numerous spherical grains (0.1–5 lm) of magne-tite and pentlandite, as well as other silicates. Geiger and Bischoff(1995) noted that one population of magnetite includes micron-sized grains dispersed throughout these meteorites. Kallemeynet al. (1991) noted widespread silicate blackening due to abundant,tiny (<0.3–10 lm) grains of magnetite and pentlandite that perme-ate the interiors of many silicates, but they did not ascribe aspecific mechanism for this. Noguchi (1993) determined silicateblackening as being due to fine-grained (mostly <few microns)magnetite. Brearley (2009) suggested that silicate blackening islikely due to shock, but that other processes may also have playeda role. Rubin (1992) noted that CKs have been shocked, opaqueswere mobilized and invaded adjacent silicates causing shock dark-ening, and then, in some cases, the meteorites were annealed tosuch an extent that the olivine crystal lattices were healed, andno longer exhibited the same shock effects that they did prior toannealing. In other words, the apparently low shock effects inolivine can be attributed to the process of post-shock annealing.Chaumard et al. (2012) suggest that small CK meteoroids withperihelia close to the Sun may have undergone transient heatingup to 1050 K.

3. Experimental procedure

Many of the details of our experimental procedure have beendiscussed in previous papers in this series (Cloutis et al.,2011a,b). A total of 15 CKs, spanning a range of petrologic grade,were included in this study (Table 3). These spectra were supple-mented with older spectra measured at other facilities (Table 3).Of the RELAB spectra, 4 had only limited spectral coverage(0.3–0.88 lm). A number of samples have reflectance spectra avail-able for multiple grain sizes (Table 3).

Briefly, reflectance spectra were measured for various size pow-ders. With the exception of Karoonda, all CK spectra were mea-

sured at the RELAB facility at Brown University, from 0.3 to2.5 lm at i = 30� and e = 0� relative to a halon standard, andcorrected for minor irregularities in halon’s absolute reflectance.Karoonda was measured by Gaffey (1974) using and integratingsphere and subsequently digitized for inclusion in the RELAB database. As in our previous studies of CCs, we have applied continuumremoval to the spectra to isolate absorption features of interest anduse various metrics of spectral slope and overall reflectance tosearch for systematic spectral-compositional trends (Cloutiset al., 2011a,b). Descriptions of the CKs included in this study areprovided in Appendix A. The reflectance spectra of the CKs are pro-vided as an on-line supplement.

We have developed a variety of easily-applicable spectral met-rics for analysis of CCs (Cloutis et al., 2011a,b), and we utilize these

914 E.A. Cloutis et al. / Icarus 221 (2012) 911–924

same metrics for analysis of CKs. These metrics include absolutereflectance at 0.56 lm, highest absolute reflectance, various mea-sures of overall spectral slope, and band depths. Band centers weredetermined by first dividing out a straight line continuum tangentto the spectra on either side of the 1 lm region feature. The centerof this feature was then fit with both third order polynomials usingdifferent numbers of data points as well as the midpoints of a ser-ies of chords spanning the absorption feature.

4. Spectral properties of constituent phases

The main constituents in CK chondrites include olivine(Fa�21–33), magnetite (with a variety of grain sizes), Fe-sulfides,pyroxene (both low- and high-Ca), plagioclase feldspar, CAIs (thatinclude a variety of minerals such as fassaite and Fe-bearing spi-nel), and minor amounts of carbonaceous phases.

CK constituents can be broadly subdivided into two varieties –those that contribute distinct spectral features, and those thataffect overall reflectance and spectral slopes. The constituents thatwill contribute spectral features include olivine, pyroxene, plagio-clase feldspar, magnetite, and CAI minerals. Of these, olivine is themost common constituent in CKs. It is characterized by anabsorption feature centered near 1.06 lm that consists of threeabsorption features due to Fe2+ crystal field transitions in the M2site (near 1.06 lm), and M1 site (near 0.85 and 1.25 lm). Withincreasing Fe2+ content, the center of this feature moves to longerwavelengths, it becomes deeper, and overall reflectance decreases(King and Ridley, 1987). The olivine band center occurs between�1.045 and 1.085 lm. Fig. 1 shows reflectance spectra of someolivine spectra as a function of Fe2+ content.

Fig. 1. Reflectance spectra of CK constituents (<45 lm grain sizes). (a) Olivines of differeand fassaites. (c) Spinels of varying FeO and Fe2O3 contents. (d) Magnetite, troilite, grmaterials represent possible analogues of carbonaceous phases in CK chondrites.

Of the other CK silicates, pyroxene can contribute Fe2+-associatedcrystal field transition absorption features near 1 and 2 lm(Adams, 1974), while plagioclase feldspar may exhibit a weakFe absorption band near 1.25 lm (Adams and Goullaud, 1978)(Fig. 1). Pyroxene abundances in CKs are generally too low com-pared to olivine to appreciably affect olivine band positions(Cloutis et al., 1986). The presence of pyroxene may be indicatedby a 2 lm region band whose position varies from �1.80 to2.08 lm for low-Ca pyroxenes, and �1.90–2.38 lm for high-Capyroxenes. Low-Ca pyroxenes are generally more abundant thanhigh-Ca pyroxenes in CKs, and are also stronger absorbers; thus,any pyroxene features seen in CK spectra will likely be attribut-able to low-Ca pyroxenes. Plagioclase feldspar is a very weakabsorber compared to olivine and pyroxene. When its lowabundance in CKs is coupled with its low optical density, andthe fact that its absorption band overlaps the stronger M1 bandof olivine near 1.25 lm, the presence of plagioclase feldspar isnot expected to be determinable from CK spectra. Magnetitehas a broad Fe2+ absorption band centered near 1 lm (Shermanet al., 1982; Fig. 1), and its spectral shape seems to be a functionof grain size and cation deficiencies (Morris et al., 1985). Of theCAI minerals that may contribute to CAI spectra, fassaite isred-sloped and only weakly featured, while Fe2+-bearing spinelhas an intense tetrahedrally-coordinated Fe2+ band located near2.1 lm (Cloutis and Gaffey, 1993; Cloutis et al., 2004; Sunshineet al., 2008) (Fig. 1).

CAI constituents that are spectrally featureless include troiliteand related Fe-sulfides, such as pentlandite, which are red-sloped(Fig. 1), and carbonaceous phases, which may be neutral or red-sloped (Johnson and Fanale, 1973).

nt Fa content. (b) Plagioclase feldspars of An contents similar to plagioclase in CKs,aphite, anthracite coal, and carbon black (<0.021 lm grain size). The latter three

Fig. 2. Reflectance spectra of fine-grained CK chondrites. (a) CK4. (b) CK4/5 andCK5. (c) CK 5/6 and CK6. Grain sizes are indicated for each spectrum.

Fig. 3. Duplicate reflectance spectra of a <180 lm fraction of ALH 85002.

E.A. Cloutis et al. / Icarus 221 (2012) 911–924 915

5. Results

Fig. 2 shows reflectance spectra of fine-grained powders of theCKs included in this study, separated by petrologic grade. As agroup, they are characterized by widely varying overall reflectance(�11–22% at the visible region peak), slightly red to blue spectralslopes beyond �0.8 lm, a ubiquitous olivine-like absorption bandin the 1 lm region, and a variable absorption feature in the 2 lm re-gion. With increasing metamorphic grade we see a possible decreasein reflectance, and a possibly deeper 1 lm region absorption feature.Specific spectral compositional trends are discussed in the nextsection.

5.1. Duplicate CK spectra

In previous papers in this series we have assessed spectral vari-ability within single CCs when duplicate spectra are available. Forthe CKs, we have duplicate spectra of a <180 lm fraction of ALH85002 (Fig. 3). For this sample, reflectance and 1 lm band depthvary by <1% absolute. Spectral slope, as measured by the visibleregion peak: 2.5 lm reflectance ratio is 1.06 and 1.14 for the twospectra (Table 4). This suggests that a single CK can have some spec-tral variability that includes differences in band depth and slope.

5.2. Grain size effects

For a number of the CKs, multiple grain sizes are available(Table 3), allowing us to assess how grain size variability affectsCK spectra. However, whether these grain size variations are fora single subsample is unknown in some cases. For EET 87526 wehave spectra of a powder of unknown grain size and a <63 lmfraction (Fig. 4a). The two spectra have similar shapes, and slopes,and overall reflectance varies by <2%. Interestingly, band minimaand centers exhibit differences; band minima are 1.121 and1.132 lm, and band centers are at 1.060 and 1.068 lm (Table 4).The difference in band centers translates into a variation in olivinecomposition of �Fa20 (King and Ridley, 1987). This is well beyondthe expected compositional variability of CKs, particularly for a sin-gle CK, suggesting that some other factors can affect absorptionband positions. These include the possibility that their somewhatdifferent overall slopes affect the effectiveness of the straight linecontinuum removal for band centers, and/or that other mineralog-ical differences, such as magnetite abundance variations, may existbetween the two samples. It is also possible that olivine absorptionbands may be saturated in the unknown size fraction spectrum,affecting band center determinations.

We have similar powder fraction spectra for EET 87860 (Fig. 4b).As with EET 87526 (above), the two spectra of EET 87860 showsmall differences in overall reflectance. The 1 lm band minimaand centers are again different between the two spectra: 1.132and 1.138 for band minima, and 1.059 and 1.072 lm for band cen-ters (Table 4). The same possibilities as described above for EET87526 may explain the differences for EET 87860.

For LEW 87009, three different spectra are available: a powderof unknown grain size, <63, and <125 lm (Fig. 4c). The powder and<125 lm spectra have similar overall reflectance and band depths,centers, and minima (varying by <2 nm). The <63 lm powder spec-trum is brighter than the other two spectra, consistent with theobservations of CCs by Johnson and Fanale (1973) that decreasinggrain size results in higher overall reflectance. Its 1 lm region bandminimum and center are both at longer wavelengths than theother two powders: 1.120 versus 1.110–1.112 lm, and 1.069 ver-sus 1.061 lm (Table 4). This supports the idea that the 1 lm regionband may saturate at moderately larger grain sizes.

Reflectance spectra of Karoonda have previously been measuredby Gaffey (1974; <150 lm) and Salisbury et al. (1975; <74 lm).

Table 4Selected spectral parameters for CK chondrites.

Meteorite Class Grain size(lm)

Reflectance at0.56 lm (%)

0.6/0.5 lmreflectance ratio

Band centernear 1 lm (lm)

Band minimum near1 lm (lm)

Depth of1 lm band (%)

�0.7 lm peak:2.5 lm refl. ratio

RELABfile ID

A-881551a CK6 <125 14.8 1.10 c1mp110A-882113a CK4 <125 11.1 1.05 c1mp109ALH 85002 CK4 Powderb 14.8 1.03 1.051 1.111 11.8 1.13 c1mb81

<125 12.6 1.02 1.060 1.127 11.1 1.26 c2mb81<25 15.9 1.06 1.063 1.111 12.6 1.04 camb8125–45 12.8 1.02 1.078 1.135 13.0 1.12 cbmb8145–75 9.9 1.00 1.063 1.135 18.0 1.32 ccmb8175–125 9.3 1.01 1.068 1.148 13.1 1.44 cdmb81<180 13.2 1.04 1.061 1.112 11.1 1.06 camh58<180 12.4 1.06 1.061 1.118 12.8 1.14 cbmh58<75 14.9 1.02 1.068 1.072 10.0 1.11 c1ph35

DAV 92300 CK4 <75 13.2 1.02 1.070 1.070 13.7 1.02 c1ph53EET 83311 CK5 <75 22.3 1.06 1.068 1.125 10.7 1.16 caph47EET 87526 CK5 Powderb 13.7 1.09 1.060 1.121 11.1 1.16 c1lm18

<63 15.3 1.11 1.068 1.132 11.2 1.19 c1mp03EET 87507 CK5 <125 12.8 1.11 1.06 1.122 13.5 1.20 c1mb92EET 87860 CK5/6 Powderb 13.3 1.02 1.059 1.132 10.9 1.24 c1lm19

<63 15.1 1.02 1.072 1.138 11.6 1.28 c1mp04EET 92002 CK4 <500 10.8 1.00 1.068 1.135 18.2 1.54 c1mc03Karoonda CK4 <150 9.6 1.03 1.048 1.062 6.7 1.03 mgp140c

<74 13 1.02 n.d. n.d. n.d. �0.93 n.a.d

LEW 87009 CK6 Powderb 18.2 1.05 1.061 1.112 25.0 1.06 c1lm17<125 17.7 1.10 1.061 1.110 31.0 1.00 c1mb88<63 22.5 1.05 1.069 1.120 24.5 1.06 camp05

PCA 91470 CK4 <75 22 1.03 1.069 1.123 14.5 1.08 c1ph46Y-693 CK4/5 <125 10.4 1.05 1.068 1.086 13.6 1.22 c1mb77Y-82102a CK5 <125 12.7 1.02 c1mp106Y-82103a CK5 <125 12.0 1.01 c1mp107

Has also been classified as an R chondrite.a Spectra only available from 0.3 to 0.88 lm.b Size not specified, but probably <125 lm.c Digitized from Gaffey (1974) – measured with an integrating sphere; not corrected for possible wavelength offset.d From Salisbury et al. (1975).

916 E.A. Cloutis et al. / Icarus 221 (2012) 911–924

Salisbury et al. (1975) noted that their sample had a reflectance of13% at 0.6 lm, a very subdued olivine absorption band, and anearly flat reflectance spectrum. We estimate band depth at 8%.The Gaffey (1974) spectrum has lower reflectance (�10% at0.75 lm) as expected given its larger average grain size, a subdued1 lm absorption band (7% deep), and is more blue-sloped over the0.7–2.5 lm interval, also as expected (Salisbury et al., 1975).

The most extensive grain size series of spectra is available forALH 85002 (Table 3). Fig. 4d shows the spectra of a progressive ser-ies of grain size intervals. With increasing grain size, the spectrabecome darker and more blue-sloped, consistent with the resultsfor other CCs (Johnson and Fanale, 1973; Cloutis et al., 2011b).Band minima move to progressively longer wavelengths (Table 4),and band centers vary but non-systematically. Again, multipleexplanations can be advanced. Band depths increase for the firstthree size fractions, from 12.6% to 18%, and then decline for the75–125 lm fraction (13.1%), suggestive of saturation for this larg-est fraction.

The other spectra of ALH 85002 (Fig. 4e) are quite similar toeach other in terms of absolute reflectance, varying by <3% abso-lute. Band minima range from 1.072 to 1.127 lm, band centersvary from 1.051 to 1.068 lm, and 1 lm region band depth variesfrom 11.1% to 12.8%. These results suggest that inclusion of the fin-est grain size fraction tends to reduce variations in absolute reflec-tance and band depths. The causes of variations in band centers arenot fully understood.

5.3. Metamorphic sequence

The CK chondrites included in this study span a wider meta-morphic range (petrologic grade 4–6) than other CCs, such as CIs,CMs, COs, CRs, and CVs. The CKs are also the only CC group that

has undergone primarily thermal, as opposed to primarily aqueous,alteration. The CK spectra are shown in Fig. 2 as a function of meta-morphic grade.

We do not find very many systematic spectral variations withmetamorphic grade. High reflectance (>15%) is seen for someCK4, 5, and 6 spectra. Band centers do not show a systematic var-iation with metamorphic grade, consistent with the narrow rangein CK olivine composition. Band minima and visible region peak:2.5 lm reflectance ratios vary but not systematically. We may haveexpected these parameters to vary systematically if thermal meta-morphism causes changes in slope. Band depths may be increasingwith increasing thermal metamorphism: the lowest band depthsare seen in the CK4–5.5 spectra, while the CK6 spectra have thehighest band depths (Fig. 5). This variation is consistent with a lossor aggregation of opaque phases at temperatures attained by theCK6 chondrites. Insufficient compositional data exists to determinewhether opaque properties, such as magnetite, sulfide, or carbonabundances vary with metamorphic grade. It should be noted thattemperatures associated with ordinary chondrite petrologic gradesmay not translate directly to CK chondrites (Noguchi, 1993).

5.4. CK4 versus CV3 (versus CO3)

Genetic relationships have been suggested between CK and CVchondrites, particularly with the CVOx subgroup. A number of CVOx

chondrites have been spectrally characterized (Table 5), and can becompared to the CK4 chondrites ALH 85002, DAV 92300, and PCA91470.

Fig. 6 shows reflectance spectra of CV3Ox and CK4 chondrites ofcomparable grain sizes. Two factors are notable from these figures.The CK4 chondrites are uniformly brighter (>12% at the visibleregion peak) than the CVOx chondrites, and have a more apparent

Fig. 4. Reflectance spectra of different size fractions of CK chondrites. (a) EET 87526. (b) EET 87860. (c) LEW 87009. (d) ALH 85002 – single grain size sequence. (e) LEW 85002– other spectra from multiple investigators. Grain sizes are indicated for each spectrum; ‘‘powder’’ refers to powdered sample of unknown grain size.

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absorption feature in the 1 lm region. Band depths are 10.0–14.5%for the CKs and 2.5–6.0% for the CVOx chondrites. These differencesare likely related, and could be attributable to thermal metamor-phism leading to a loss or aggregation of opaque phases. Thiswould lead to an increase in reflectance and a greater apparentolivine band depth – an increase in olivine abundance is notrequired for its band depth to increase.

The presence of finely-dispersed opaque phases in CK olivinehas been noted by many investigators (e.g., Kallemeyn et al.,1991; Rubin, 1991, 1992; Noguchi, 1993; Geiger and Bischoff,1995). Their origin is uncertain, and different investigators attributethem to shock (Rubin, 1992) or other processes, such as oxidationof olivine (Scott et al., 1992). The higher reflectance and deeper1 lm region absorption band in CKs versus CVs is not consistentwith shock processes, which tends to lower absolute reflectanceand weaken absorption bands, but is consistent with thermal

annealing, which may have occurred after a shock event (Rubin,1992).

5.5. CKs versus heated Allende

Further insights into whether thermal metamorphism canaccount for differences between the CVOx and CK chondrites canbe gleaned from studies of the Allende CV3Ox chondrite subjectedto laboratory heating. Figs. 7a and b show <63 lm fractions of Al-lende compared to <75 lm spectrum of the darkest CK4 chondriteDAV 92300 (<75 lm grain size). The closest spectral match appearsto be Allende heated to 1100 �C, in terms of band depth in the 1 lmregion (11.5% versus 13.7%) and overall reflectance. Allende sam-ples heated to <1100 �C all have lower reflectance and a shallower1 lm band than the CK4 spectra (unheated Allende has a 1 lmregion band depth of 5.3%). Allende heated to 1200 �C is much

Fig. 5. Band depth of 1 lm region absorption feature versus metamorphic grade forall CK spectra.

Table 5CVOx chondrites that have been spectrally characterized in previous studies.

Meteorite Subtype Petrologicsubgraderangea

Averagepetrologicsubtypeb

Petrologicsubtypeb

ALH 84028 CV3OxA 3.2 3.2ALH 85006 CV3Ox

Allende CV3OxA 3.1–3.6 3.2 >3.6Grosnaja CV3OxB 3.0–3.3 3.3 �3.6Mokoia CV3OxA 3.0–3.3 3.2 �3.6Y-86751 CV3OxA–OxB

a Guimon et al. (1995).b Bonal et al. (2006).

Fig. 6. Reflectance spectra of CVOx carbonaceous chondrite powders and CKchondrites. (a) <125 lm CVOx spectra. (b) Other grain size CVOx spectra. (c)<75 lm CK4 spectra.

918 E.A. Cloutis et al. / Icarus 221 (2012) 911–924

brighter and has a much deeper (45%) absorption band than theCK4 spectra, suggesting CK chondrites attained temperatures of<1200 �C. Spectral slopes overlap between heated Allende andthe CK chondrites.

When the CK4s are compared to naturally thermally metamor-phosed CCs (Fig. 7c), that have been heated to high temperatures,the latter are consistently darker and have shallower absorptionbands than the CKs. Temperature estimates for these thermallymetamorphosed chondrites range from 600 to 900 �C for B-7904,700–850 �C for Y-86720, and >700 �C for Y-86789 (Akai, 1990,1992, 1994; Akai and Tari, 1997; Lipschutz et al., 1999; Tonuiet al., 2002; Nakamura, 2005, 2006; Nakamura et al., 2006; Nakatoet al., 2009). These are all lower than the 1100 �C temperatureimplied for converting a CV3 to a CK4-like spectrum from theheated Allende sample spectra, suggesting that the temperaturesattained by the naturally thermally metamorphosed CCs wereinsufficiently high or of too low a duration to result in loss/aggregation of opaques, thermal annealing, or recrystallization ofsufficient olivine from pre-existing phyllosilicates.

These results suggest that CK chondrites could be producedfrom CV precursors, or possibly other CC precursors, provided theyare heated to temperatures of between �1000 and �1200 �C. Thisalso highlights the fact that while many unmetamorphosed carbo-naceous chondrites (e.g., CV) and the CK chondrites have spectrathat are dominated by olivine, they can differ in many respects.

Temperature estimates for CK chondrites are few and disparate.Chaumard et al. (2011) suggested an upper temperature limit of800 �C for the TNZ 057 CK4 chondrite on the basis of the presenceof grossular in its CAIs (the upper limit for grossular stability). Neffand Righter (2006) suggested that peak temperatures experiencedby CK6 chondrites were <610 �C because of the presence of pent-landite. Geiger and Bischoff (1995) used various petrologic andcompositional criteria to estimate metamorphic temperatures for

CKs as follows: 550–650 �C (CK4), 650–800 �C (CK5), and 800–1000 �C (CK6). Noguchi (1993) notes that petrologic classifications,that were developed originally for ordinary chondrites, may nottranslate directly to CKs; i.e., that they did not experience similarthermal histories. He also suggests that CK4 and 5 chondrites expe-rienced higher metamorphic temperatures than other chondritesbelonging to the same petrologic type.

5.6. Falls versus finds

The majority of CK chondrites are finds, largely from Antarctica.Karoonda is the only fall included in this study. Terrestrial weath-ering has been found to affect CC reflectance spectra for a numberof classes, particularly the CR chondrites (Cloutis et al., 2012a),which are spectrally quite featureless. Terrestrial weatheringeffects include the formation of various iron oxyhydroxides from

Fig. 7. Reflectance spectra of heated Allende <63 lm powders and thermallymetamorphosed carbonaceous chondrites versus <75 lm DAV 92300 CK4 spec-trum. (a) Allende spectra from top to bottom: 400 �C, unheated, 600 �C, 500 �C, and700 �C. (b) Same as (a) for Allende samples heated to between 800 and 1200 �C. (c)Thermally metamorphosed carbonaceous chondrites; grain sizes are indicated foreach spectrum.

Fig. 8. Continuum-removed spectra showing the 1 lm region of representativeCK4, 5, and 6 chondrites.

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preexisting Fe-bearing phases, such as olivine and metal. The maineffect of this type of terrestrial weathering is to cause the appear-ance of an absorption edge near 0.55 lm, and an Fe3+ absorptionband in the 0.8–0.9 lm region.

Terrestrial weathering of CKs was examined by Kallemeyn et al.(1991). They found that visual evidence of terrestrial weatheringvaried widely in CKs, some showed evaporite deposits on exposedsurfaces, while interior visible alteration ranged from rare brown-staining of silicates to pervasive staining, and the presence of cav-ities interpreted to reflect the loss of material by leaching. Theyalso found veins of Ni-rich, Mg-sulfates, brown staining around lar-ger magnetite grains and of the groundmass, minor staining oflarge olivine phenocrysts, and coarse limonite grains. They also

interpreted low pentlandite abundances as being due to weather-ing loss. Rubin and Huber (2005) developed a terrestrial weather-ing index for CKs based largely on transmitted light observations,specifically brown staining due to mobilization of oxidized iron.Their index ranges from wi-0 (<5 vol.% staining) to wi-6 (signifi-cant replacement of mafic silicates by phyllosilicates). The CKs inour study for which weathering indices have been determinedare all wi-0 or wi-1. Thus, we are not able to examine weatheringeffects on CKs in a rigorous way. However, this is offset by the factthat most of our CKs are relatively pristine, allowing us to betterexamine the spectral properties of CKs.

We compared Karoonda to other CK4 chondrites to determinewhether the finds have been affected by terrestrial weathering.The 0.6/0.5 lm ratio has been found to be an indicator of terrestrialoxidation for ordinary chondrites (Salisbury and Hunt, 1974).While the authors caution against the use of this ratio as an indica-tor of terrestrial weathering for CCs, we have found that it doesprovide some measure of terrestrial alteration. The 0.6/0.5 lmratio for Karoonda is 1.02–1.03, and 1.00–1.06 for CK4 finds, sug-gesting that terrestrial weathering has not appreciably affectedour Antarctic CKs. Many of the other terrestrial weathering effects,such as loss of pentlandite, would not be spectrally detectable.

A search of the CK spectra for evidence of terrestrial oxidation inthe form of formation of Fe oxyhydroxides failed to reveal convinc-ing evidence for these phases. Some of the spectra, such as EET87526 and EET 87507 show a weak inflection near 0.5 lm, butno sign of an additional absorption feature in the 0.8–0.9 lmregion, suggesting that terrestrial weathering spectral effects inthe available CKs is minor at best.

6. Discussion

The absorption features seen in the CK spectra are consistentwith olivine being the major contributor. This can be seen moreclearly in continuum-removed CK spectra (Fig. 8). The 1 lm regionshows the major 1.05 lm olivine M2 band, as well as the prominent1.25 lm M1 band, and a less apparent M1 band near 0.9 lm.Whether other CK constituents are contributing to absorption inthis region, such as low-Ca pyroxene (0.9 lm) and plagioclase feld-spar (1.25 lm) cannot be assessed, but their abundances in CKs aregenerally too low for them to be major contributors.

The dominance of olivine is also apparent from the continuum-removed band centers. They range from 1.051 to 1.078 lm(Table 4), within the range expected for olivine and broadly consis-tent with CK olivine composition (King and Ridley, 1987). Asdiscussed above, band minima are more wide-ranging, from1.062 to 1.148 lm and are affected by overall continua slopes,

Fig. 9. Reflectance spectrum of <125 lm fraction of the Y-693 CK4/5 chondriteshowing an absorption feature near 2.2 lm that is evidence of the presence of Fe-spinel.

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which straight line continuum removal is reasonably effective atremoving. It was also noted above that increasing grain size(for ALH 85002) correlates with an increasingly blue slope andincreasing band minimum position.

In comparison to pure olivine of equivalent grain size to the CKspectra, the CK spectra are darker. This is attributable to the abun-dant fine-grained opaques in CKs, the most abundant being mag-netite and sulfides. The blue slope of many of the CK spectra islikely attributable to the Fe-bearing spinels and/or magnetite.Sulfides are red sloped, while carbonaceous phase abundancesare likely too low to induce a blue slope; however the spectralproperties of this material are unknown, but are likely neutral tored-sloped (Johnson and Fanale, 1973).

Beyond the fact that the CK6 chondrites seem to have a deeper1 lm absorption band than the CK4–5.5 chondrites (Fig. 5), noother spectral-compositional trends were found. The CK6 chon-drites do not differ from the lower grade CKs in terms of band min-ima or centers, 0.6/05 lm ratios, or visible region peak: 2.5 lmratios. This may be due in part to the limited sample size, as wellas variations in magnetite and CAI abundances that do not appearto be correlated with CK metamorphic grade. Therefore, all that canbe said concerning CKs is that their spectra are dominated by oliv-ine, are brighter and have a deeper 1 lm region absorption bandthan CV chondrites (for equivalent grain sizes), and spectral slopescan vary from red to blue. A more detailed comparison of CKs toother CCs is the subject of a future paper in this series.

6.1. CAI spectral contributions

As discussed above, CAI abundances are very variable in CKs,with abundances ranging upward of 10 area or vol.%. A numberof factors suggest that CKs may show spectral evidence of CAIs,specifically due to Fe-bearing spinel, in the 2 lm region. Thisincludes:

1. the high abundance of CAIs in some CKs;2. the fact that a number of CO and CV chondrites, which have CAI

abundances equivalent to some CKs, show evidence of spectralcontributions in the 2 lm region (Cloutis et al., 2012b,c);

3. the low abundance of pyroxene in CKs should not result in addi-tional or possible interfering pyroxene absorption bands in thisregion;

4. the presence of Fe in CK CAI spinels (Noguchi, 1993) should leadto intense absorption bands near 2.1 lm (Cloutis et al., 2004),provided spinel abundances are high enough to result in mea-surable absorption bands.

If CKs are derived by thermal metamorphism from CVs, and if Fecontent of CAI spinels is greater in more metamorphosed CKs, wewould expect CKs to exhibit more prominent Fe-spinel absorptionbands than CVs. Chaumard et al. (2009) found Fe enrichment infine-grained CAIs with increasing metamorphism in CK3s andCK4, although where this Fe is located in the CAIs was not speci-fied. It has been suggested that CAIs are rare in CK chondrites(McSween, 1977; Kallemeyn et al., 1991; Hezel et al., 2008),although some CKs have CAI abundances in excess of 10% (e.g., Neffand Righter, 2006; Chaumard et al., 2011). For example, Neff andRighter (2006) determined that EET 87860 has 10.7 modal% CAIs.

Few of the CKs in our study have determined CAI abundances.The CK spectra that should show evidence of CAI/spinel spectralfeatures are EET 87860, which contains �11 vol.% CAIs (Neff andRighter, 2006), and LEW 87009, which is the most metamorphosedCK (Kallemeyn et al., 1991), and which may be expected to containmore Fe in its CAIs. The EET 87860 spectra are suggestive of thepresence of Fe-spinel by the fact that their spectra are blue-slopedbeyond �1.5 lm; pure olivine spectra are flat in this region. We

could invoke the possibility that the blue slope could be causedby other phases in this meteorite, however spinel remains the mostplausible cause of the reflectance decline over the 1.5–2.5 lminterval. LEW 87009 has a very olivine-like spectrum, being flatbeyond�1.7 lm. Its CAI abundance is unknown and does not showevidence of Fe-spinel: a prominent absorption band in the 2.1 lmregion. CAIs appear to be rare or to occur as scattered large discreteinclusions in CKs (e.g., Noguchi, 1993; Pratesi et al., 2006; Brearley,2009). It is possible that the samples of EET 87860 and LEW 87009used in this study may have excluded large CAIs.

A number of the other CK spectra exhibit a reflectance declinelongward of �1.5 lm, which is consistent with spectral contribu-tions from Fe-spinel, including ALH 85002 (<75 and <125 lm spec-tra), EET 83311, EET 87526, EET 92002, and Y-693. Of these, Y-693exhibits the best evidence for an Fe-spinel absorption band, show-ing an absorption feature near 2.2 lm superimposed on the reflec-tance decrease (Fig. 9).

7. Implications for asteroids

Greenwood et al. (2010) suggested that because CVs and CKsmay form a compositional continuum, and have similar cosmicray age distribution, they may derive from a common parent body.They suggested the Eos asteroid family as a possible source.Mothé-Diniz et al. (2008) examined reflectance spectra of a num-ber of Eos family members and noted that CK4 and CK5 spectraare a good analogue to many Eos family members in the near-infra-red (0.8–2.5 lm), but differed in the visible region, with the CKspectra having more rounded maxima near 0.7 lm. They alsonoted that other olivine-bearing meteorites, such as R-chondritesare also good or better matches to many Eos family asteroids. Theyalso found that MGM fitting (Sunshine et al., 1990) required theinclusion of low-Ca pyroxene to provide acceptable fits. Albedoswere not used in their analysis, but all of the Eos family membersused in their analysis have albedos consistent with CKs, whose0.56 lm reflectance ranges from 9.6% to 22.5%. These results col-lectively suggest that CKs are not the best spectral analogues forEos family members. It is also worth noting that a number of mete-orite classes (CV, CK, CO, R) have olivine-dominated lithologies.However, we also note that many Eos family member spectra areblue-sloped beyond�1.5 lm, similar to many of the CK chondrites.

8. Summary and conclusions

CK chondrite reflectance spectra are characterized by a ubiqui-tous absorption feature in the 1 lm region that is attributable to

E.A. Cloutis et al. / Icarus 221 (2012) 911–924 921

olivine. The center of this band is broadly consistent with the com-position of CK olivine, although it should be noted that the olivineband center varies by only �40 nm from Fa0 to Fa100 (King andRidley, 1987). CAIs, which are present in variable amounts inCKs, do not normally result in a well-defined absorption band thatcan be related to Fe-bearing spinel; i.e., an absorption band cen-tered near 2.1–2.2 lm. However, CAIs may be causing a numberof CK spectra to be blue-sloped beyond �1.5 lm. No good spectralcorrelations have been found to determine metamorphic grade,although it appears that olivine band depths are greatest in theCK6 group. This could be related to various factors such as loss/aggregation of opaques that may accompany metamorphism.

A number of investigators have suggested linkages between CVand CK chondrites (e.g., Greenwood et al., 2003, 2004, 2010;Devouard et al., 2006; Isa et al., 2011). Spectrally it appears thatfine-grained CVs are darker than CKs and have shallower olivineabsorption bands. CVs also generally have more well-definedCAI-associated absorption features in the 2 lm region. If CKs arethermally metamorphosed CVs, heating temperatures of between�1000 and �1200 �C are required for CVs (at least for the case ofAllende) to match CK spectra in terms of overall reflectance andolivine band depth. These temperatures appear to be at odds withmany CK temperature estimates based on mineralogic and petro-logic criteria, which are much lower. CCs that have been naturallythermally metamorphosed (up to �950 �C) are darker than CKspectra. They also do not have well-defined olivine absorptionbands, suggesting that they were not heated to high enough tem-peratures to reduce the spectrum-darkening effects of opaques orto recrystallize from pre-existing phyllosilicates.

With increasing grain size (and excluding the finest fraction),CK spectra become darker and more blue-sloped, and as a resultthe band minimum in the 1 lm region moves to longer wave-lengths. These observations are consistent with the behavior ofother CCs (Johnson and Fanale, 1973).

Acknowledgments

We wish to thank the invaluable and generous assistance pro-vided by many individuals which made this study possible. In par-ticular we thank the US and Japanese Antarctic meteorite programsfor recovering the majority of the samples included in this study.The RELAB facility at Brown University is a multi-user facility oper-ated with support from NASA Planetary Geology and GeophysicsGrant NNG06GJ31G, whose support is gratefully acknowledged.This study was supported by an NSERC Discovery grant to EAC.We also wish to thank Alan Rubin and Beth Clark for their cogentand valuable comments which improved the accuracy and read-ability of this manuscript.

Appendix A. Descriptions of CKs included in this study

A.1. A-881551 (CK6)

This meteorite has been classified as a CK6 chondrite byChikami et al. (1998) on the basis of absence of CAIs, recrystallizedmatrix, blurring of chondrules, low abundance of chondrules(11 vol.%), homogenous olivine (Fa33), a matrix composed largelyof coarsely recrystallized olivine, plagioclase, compositionallyhomogeneous augite, pentlandite, pyrite, and a high abundanceof magnetite with ilmenite and spinel lamellae. It contains5.3 wt.% FeS, 0 wt.% Fe–Ni metal and 2.0 wt.% H2O (Yanai et al.,1995), Olivine composition is Fa32.7–34.8 (average Fa33.5) (Yanaiet al., 1995). Hirota et al. (2002) classified it as a CK6, presumablyon the basis of REE abundances.

A.2. A-882113 (CK4)

This meteorite was classified as C4 by Yanai et al. (1995) andCK4 by Hirota et al. (2002), presumably on the basis of REE abun-dances. Olivine composition is Fa21.4 (range Fa20.0–22.8); pyroxenecomposition is Fs22.6 (range Fs20.0–27.3); high-Ca pyroxene thatwas detected is Fs8.3 Wo45.3 (Yanai et al., 1995). It also contains pla-gioclase feldspar and high-Ca pyroxene (Yanai et al., 1995). It con-tains 4.7 wt.% FeS, 0 wt.% Fe–Ni metal and 3.1 wt.% H2O (Yanaiet al., 1995).

A.3. ALH 85002 (CK4; weathering index-1; weathering grade A)

This meteorite was initially classified as a C4 by Martinez andMason (1986). The interior is light gray with dark rounded inclu-sions and white irregular-shaped inclusions (Martinez and Mason,1986). In thin section it consists largely of olivine, with a littlepyroxene, plagioclase and opaques (largely magnetite) (Martinezand Mason, 1986). A few olivine-bearing chondrules are present;compositions are: olivine Fa29, pyroxene Fs26, and plagioclaseAn54–59 (Martinez and Mason, 1986). Mason (1991) described itas consisting of finely-granular olivine (Fa29), small amounts ofpyroxene (Fs26), plagioclase (An54–59), and opaques (largely magne-tite), and a few olivine-rich chondrules. Olivine and low-Ca pyrox-ene compositions are Fa�30 and Fs23–29 according to Kallemeynet al. (1991). Opaque phases include sulfides and magnetite (Kalle-meyn et al., 1991). It contains 3.7 modal vol.% magnetite and 0.6modal vol.% sulfides (Geiger and Bischoff, 1995). Non-stoichiome-tric magnetite constitutes �20% of the iron modal mineralogy(Fisher and Burns, 1991). C and S contents are 0.006 and1.86 wt.%, respectively (Hartmetz et al., 1989).

A.4. DAV 92300 (CK4; weathering grade A/B)

This meteorite was classified as a CK4 chondrite by Marlow andMason (1993a). Magnetic susceptibility measurements for thismeteorite are consistent with CK chondrites (Rochette et al.,2008). It contains numerous chondrules in a medium-gray fine-grained matrix (Marlow and Mason, 1993a). It contains small(0.01–0.05 mm) olivine grains and minor opaque material with afew chondrules; olivine composition is Fa26; minor pyroxene isFs26 (Marlow and Mason, 1993a). The opaque mineral is largelymagnetite (Marlow and Mason, 1993a).

A.5. EET 83311 (CK5; weathering index-1; weathering grade A/B)

This meteorite consists largely of finely granular olivine (Fa31)and minor magnetite and is medium to dark gray in color (Scoreand Mason, 1987). The interior is medium to dark gray with abarely visible chondritic structure (Score and Mason, 1987). It iscomposed largely of finely granular olivine and a little plagioclaseand opaques (largely magnetite) (Score and Mason, 1987). Itcontains 6.6 modal vol.% magnetite and 0.5 modal vol.% sulfides(Geiger and Bischoff, 1995). It was reclassified from a C4 chondriteto a CK5 chondrite by Score and Lindstrom (1994). Olivine compo-sition is Fa�33 according to Kallemeyn et al. (1991). Opaque phasesinclude sulfides and magnetite (Kallemeyn et al., 1991). C and Scontents are 0.04 and 1.98 wt.%, respectively (Hartmetz et al.,1989).

A.6. EET 87526 (CK5; weathering grade Be)

It was initially classified as a C4 chondrite (Martinez et al.,1988). The interior of this meteorite is fine-grained and light todark gray, with abundant dark inclusions (Martinez et al.,1988). A thin section shows an aggregate of small olivine grains

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and a little opaque material with sparse chondrules; olivine isFa29 and it also contains a little pyroxene (Fs24 Wo1) and plagio-clase (An49); the opaque material is mainly magnetite with a lit-tle pentlandite (Martinez et al., 1988). Non-stoichiometricmagnetite constitutes �20% of the iron modal mineralogy (Fisherand Burns, 1991). C and S contents are 0.007 and 1.9 wt.%,respectively (Hartmetz et al., 1989). It may be paired with EET87507 (Martinez et al., 1988).

A.7. EET 87507 (CK5; weathering index-1; weathering grade B)

It was initially classified as a C4 chondrite (Martinez et al.,1988). The interior of this meteorite is fine-grained and light todark gray, with abundant dark inclusions, and may be paired withEET 87526 (Martinez et al., 1988). See EET 87526 (above) for adescription. It contains 3.1 modal vol.% magnetite and <0.1 modalvol.% sulfides (Geiger and Bischoff, 1995). Olivine and low-Capyroxene compositions are Fa�32 and Fs28 according to Kallemeynet al. (1991). Olivine composition is homogeneous around Fa30

(Noguchi, 1993). Both low and high-Ca content pyroxenes are pres-ent. Low-Ca pyroxene compositions average Fs26 Wo2; high-Capyroxenes average Fs10 Wo44; Karoonda has more heterogeneousmafic silicates than Y-693 and EET 87507 (Noguchi, 1993). It con-tains vesicular olivine containing numerous small (<0.1–5 lm)grains of magnetite and pentlandite formed by shock melting(Hashiguchi et al., 2008). Opaque phases include sulfides andmagnetite (Kallemeyn et al., 1991). It was reassigned to CK4 onthe basis of the presence of well-defined chondrules (Marlowet al., 1992), and later to CK5 by Score and Lindstrom (1994). Arealabundance of CAIs is 0.2% (Hezel et al., 2008).

A.8. EET 87860 (CK5/6; weathering index-1; weathering grade A/B)

It was initially classified as a C5 chondrite by Martinez andMason (1988). It is light gray and very fine-grained, with threeprincipal minerals: a mafic mineral, white plagioclase, and sulfide(�5–10%); no chondrules are visible (Martinez and Mason, 1988).A thin section shows an aggregate of olivine and minor plagio-clase, with a small amount of finely-dispersed opaque material(magnetite and pentlandite) (Martinez and Mason, 1988). Thismeteorite contains 7 vol.% chondrules, 12 vol.% opaques,11 vol.% CAIs, and 71 vol.% matrix (Neff and Righter, 2006).Olivine composition is Fa28; (Grossman, 1994) pyroxene wasnot detected, and plagioclase is variable (An21–72) (Martinez andMason, 1988). Olivine and low-Ca pyroxene compositions areFa�30 and Fs28 (Kallemeyn et al., 1991). Opaque phases includesulfides and magnetite, and Fe–Ni metal is absent (Kallemeynet al., 1991; Neff and Righter, 2006). It contains 3.9 modal vol.%magnetite and 0.6 modal vol.% sulfides (Geiger and Bischoff,1995). Mössbauer analysis suggests that non-stoichiometricmagnetite constitutes �20% of the iron modal mineralogy (Fisherand Burns, 1991). It contains vesicular olivine containing numer-ous small (<0.1–5 lm) grains of magnetite and pentlanditeformed by shock melting (Hashiguchi et al., 2008). It contains0.03 wt.% C (Jarosewich, 1990).

A.9. EET 92002 (CK4; weathering grade A/Be)

This meteorite was classified as CK4 by Marlow and Mason(1993b). The interior matrix is dark gray and it consists of anaggregate of small olivine grains and minor opaque materials withoccasional chondrules (Marlow and Mason, 1993b). Olivine com-position is Fa32, and it also contains a little diopside and plagio-clase. The opaque mineral is largely magnetite, and it may bepaired with EET 87507 (Marlow and Mason, 1993b). It contains0 wt.% water-soluble C (Mautner, 2008).

A.10. Karoonda (CK4; weathering index-0; fall)

Karoonda contains 6.8 modal vol.% magnetite and 1.3 modalvol.% sulfides (Geiger and Bischoff, 1995), and 15 vol.% chondrules(Scott and Taylor, 1985). Areal abundance of CAIs is 5.74% (Hezelet al., 2008). Mason and Wiik (1962) describe Karoonda as having(in wt.%) 70% olivine, 9% plagioclase, 8% pigeonite, 8% magnetite,4% pentlandite, and 1% sulfides. The matrix is largely composed ofolivine, heavily decorated with micron-sized magnetite and minorsulfides (Scott and Taylor, 1985). Olivine and low-Ca pyroxenecompositions are Fa�31 and Fs26–28 (Kallemeyn et al., 1991). Olivinecomposition clusters around Fa33 (Mason, 1963; Van Schmus,1969), or Fa34.2 (Fitzgerald, 1979), with a compositional range ofFa25–35 (Noguchi, 1993) or Fa�15–32 (Scott and Taylor, 1985). Bothlow- and high-Ca content pyroxenes are present. Low-Ca pyroxenecompositions are Fs8–28 Wo0–5; (or Fs6–25 – Scott and Taylor, 1985);high-Ca pyroxenes are Fs4–16 Wo39–50; Karoonda has more hetero-geneous mafic silicates than Y-693 and EET 87507 (Noguchi,1993). Opaque phases include sulfides and magnetite (Kallemeynet al., 1991). The principal opaque phases are chromian magnetiteand sulfide according to Fitzgerald (1979). Its matrix is recrystal-lized (McSween, 1977). Mössbauer analysis indicates that non-stoichiometric magnetite constitutes�20% of the iron modal miner-alogy (Fisher and Burns, 1991). Bulk C content is 0.07 wt.% (Pearsonet al., 2006), and S content is 1.4 wt.% (Fitzgerald, 1979).

A.11. LEW 87009 (CK6; weathering index-1; weathering grade Ae)

It was initially classified as a C6 chondrite by Schwarz and Ma-son (1988) and CK6 by Score and Lindstrom (1994). The interior isgreenish-gray with no clasts evident (Schwarz and Mason, 1988). Athin section shows an aggregate of olivine grains with minor pla-gioclase, blebs of magnetite are scattered throughout, traces of sul-fide are present, and some silicates have a vague chondritic form(Schwarz and Mason, 1988). It contains 0 vol.% chondrules,4 vol.% opaques, and 79 vol.% matrix (Neff and Righter, 2006), 4.6modal vol.% magnetite and 0.7 modal vol.% sulfides (Geiger andBischoff, 1995). Compositions are: olivine Fa31; one augite grainis Fs12 Wo44 (Schwarz and Mason, 1988). Olivine composition isFa�32 according to Kallemeyn et al. (1991). Magnetite and Fe sul-fides are present while Fe–Ni-metal is absent (Kallemeyn et al.,1991; Neff and Righter, 2006). Mössbauer analysis indicates thatnon-stoichiometric magnetite constitutes �20% of the iron modalmineralogy; its Mössbauer spectrum is dominated by magnetiteand Fe2+ in olivine (Fisher and Burns, 1991). It contains 0.04 wt.%C (Jarosewich, 1990).

A.12. PCA 91470 (CK4; weathering grade A/B)

The interior of this meteorite is light colored with a fine-grainedmatrix and several dark inclusions (Marlow and Mason, 1993c). Athin section shows an aggregate of olivine grains and minor opa-que material (consisting of magnetite and pentlandite) and a fewchondrules (Marlow and Mason, 1993c). The olivine compositionis Fa33 and a few grains of plagioclase were also analyzed(An50–60); it was classified as a CK4 chondrite by Marlow andMason (1993c).

A.13. Y-693 (CK4/5; weathering index-0)

A classification of CK5 was suggested by Nakamura et al. (1993),and C4 by Yanai et al. (1995). Its modal composition is 8% plagio-clase, 4% Ca-rich pyroxene, 3% low-Ca pyroxene, 65% olivine, 9%magnetite, 1.5% metal, and 3.6% troilite, and it contains 5 vol.%chondrules (Okada, 1975). Modal abundances (from point count-ing) are 2.1 vol.% pyroxene, 63.5 vol.% olivine, 11.5 vol.%

E.A. Cloutis et al. / Icarus 221 (2012) 911–924 923

plagioclase, and 22.9 vol.% opaque minerals (Okada, 1975). It con-tains 11 vol.% recognizable chondrules (Nakamura et al., 1993). Thematrix is composed of homogenous olivine, plagioclase, and finely-dispersed opaques (Okada, 1975). Olivine (homogeneous: Fa29–30)and plagioclase are the major matrix constituents, with minorlow-Ca pyroxene, magnetite and pentlandite according toNakamura et al. (1993). Both low and high-Ca content pyroxenesare present (Noguchi, 1993). Olivine and low-Ca pyroxene compo-sitions are Fa�29 and Fs26, respectively (Kallemeyn et al., 1991), orFa28–32, average Fa29, and Fs24–26, respectively (Yanai et al., 1995).Olivine composition is homogeneous around Fa34 according toNoguchi (1993), or averages Fa30 (Okada, 1975). Low-Ca pyroxenecompositions average Fs26 Wo2 and high-Ca pyroxenes averageFs10 Wo44; Karoonda has more heterogeneous mafic silicates thanY-693 and EET 87507 (Noguchi, 1993). Chondrule olivine andpyroxene are very homogenous, Fa29–31 and Fs25–28, respectively(Nakamura et al., 1993). Opaque phases include sulfides and mag-netite (Kallemeyn et al., 1991), with magnetite and pentlandite asthe major opaque phases, and a small amount of troilite (Okada,1975). It contains 4.2 wt.% FeS and 0 wt.% Fe–Ni metal (Yanaiet al., 1995). It contains 5.7 modal vol.% magnetite and 0.8 modalvol.% sulfides (Geiger and Bischoff, 1995). Saturation magnetiza-tion measurements indicate that magnetite is the major opaquemineral along with a very small amount of metal (Okada, 1975).Magnetite is abundant as micron-sized grains dispersed in bothchondrules and matrix (Nakamura et al., 1993). It contains0.06 wt.% C and 1.6 wt.% S (Gibson and Yanai, 1979), and0.18 wt.% H2O (Yanai et al., 1995). It exhibits pronounced silicateblackening due to widely dispersed magnetite grains (Nakamuraet al., 1993).

A.14. Y-82102 (CK5; weathering index-0)

Olivine composition is Fa28.3–30.7 (average Fa29.5), and pyroxenecomposition is Fs23, high-Ca pyroxene that is present is Fs9.3 Wo41.3

(Yanai et al., 1995). Righter and Neff (2007), Hirota et al. (2002) andRubin and Huber (2005) categorized it as a CK5. It may be pairedwith Y-82103 (Rubin and Huber, 2005).

A.15. Y-82103 (CK5; weathering index-0)

Olivine composition is Fa28.7–34.9 (average Fa29.8), and pyroxenecomposition is Fs25.1, high-Ca pyroxene that is present is Fs17.9

Wo22.2 (Yanai et al., 1995). Righter and Neff (2007) and Rubinand Huber (2005) categorized it as a CK5. It may be paired withY-82102 (Rubin and Huber, 2005).

Appendix B. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.icarus.2012.09.017.

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